The prior art devices adapted for use in aeration of waste materials have predominantly employed spargers, such as, perforated pipe and the like for releasing the oxygen bearing gas in the bottom of the storage tank or holding pond. The dispersion of the released gases from the sparger occasionally is further agitated by rotating vanes or multiple level baffles within the storage tank. For example, an arrangement for introducing the oxygen bearing gas in line with a propeller agitator is shown in U.S. Pat. No. 3,865,721 to Kaelin. Other efforts to directly agitate a fluid by releasing pressurized gas below the fluid surface and into flow directing columns are shown in U.S. Pat. Nos. 1,574,783 to Beth, 3,043,433 to Singer and 3,446,488 to Mail et al.
It has also been known for some time to use a pressure differential injector for drawing gas into a liquid stream as is shown in U.S. Pat. No. 1,430,303 to Hartman while similar such injector/mixer apparatus for other applications are shown in U.S. Pat. Nos. 3,243,046 to Kakumoto et al and 214,090 to Bott. Although specifically concerned with steam condensation, the device of Bott includes a spiral ridge arrangement within the outlet horn. Other patents of interest are U.S. Pat. Nos. 2,479,403 to Powers, 3,306,449 to Minigishi, 3,833,719 to Kuerten et al, 3,671,022 to Laird et al, and French Pat. No. 452,874.
The use of spargers and other devices in oxygenation of wastes generally recognizes that a larger bubble which tends to rise rapidly to the surface of the liquid expels much of its liquid treating contents (usually oxygen) uselessly into the atmosphere. Thus it is important that the gas be reduced to bubbles of the smallest possible size prior to release thereby permitting a higher percentage of the oxygen content within the bubbles to be transferred into the liquid. In providing oxygen for an aerobic system, air flow as is generally measured in cubic feet per minute (cfm) is highly important as it requires approxiamtely 65 cubic feet of air for each pound of oxygen. A traditional rule of thumb relative to mechanical areation systems is that two pounds of dissolved oxygen (DO) per horsepower hour is the expected level of recovery through such prior art systems and the economic penalty for aerobic digestion of wastes generally has increased as power costs have increased. Further, the power requirements to overcome the hydraulic head of relatively deep containers or storage ponds, such as, up to a depth of about 20 feet often pose further economic disadvantage for the prior art diffuser systems. Venturi-type devices for intermingling of gases and fluids, such as, Minigishi have been more for the purpose of agitation accomplished by release of the air bubbles at the surface and have not been accepted for meeting the continuous emulsification and large volume mixing demanded by waste treatment facilities.
Accordingly, there has been a continuing need for economic and efficient methods and apparatus of gas/fluid intermingling adequate to meet the demands for odor control as in the use of anaerobic ponds and especially to meet the stringent regulations concerning effluence entering rivers and streams. In this same relation, it has been recognized that magnesium phosphate deposition on metal surfaces is a particular problem in the course of recycling anaerobic liquid from animal waste treatment lagoons; and, if not properly controlled, there is a tendency for the particles to collect and form a scale on the pump impeller and other surfaces through which the liquid is directed so as to impose severe limitations on the life of the equipment and to some extent affect the quality of digestible protein recovered. Various magnetic and electromagnetic collectors have been employed either alone or in connection with chemical flocculating agents to remove metallic or mineral particles in liquids but none devised for use in association with a pump impeller or submersible inductor assembly so as to create a magnetic field across an inlet passage for the removal of particles from animal waste material so as to enhance the efficiency and performance of the inductor assembly in the aerobic digestion of fines in the material and conversion into single cell protein. Representative patents of interest are U.S. Pat. Nos. 3,697,420 to D. S. Blaisdell et al; 3,714,037 to G. C. Almasi et al; 3,936,376 to P. Centineo; 3,998,741 to G. D. Councell; 4,278,549 to J. L. Abrams et al; 4,279,748 to K. Inoue; 4,289,621 to J. R. O'Meara, Jr.; and 4,299,700 to C. H. Sanderson.